we don't use OpenVPN on the PFSense. We only use IPSec.
I don't know, why it will be displayed in the logs.

The same is the gateway. We have a static public IP address
and don't use a dyndns gateway.

Oh ok thank you for providing this information, I was a little bit confused on this entries and was
not really able what I should think on, thanks again for the clarification on this.

I have another one for you, you where telling us that all was running fine for you and also
the VPN connections before upgrading to a higher pfSense version, is this right? Perhaps,
only perhaps I mean you or somebody was doing or making custom set up entries and after
the update or upgrade was done all files was new written and this custom made settings were
gone. And now the set up is not really fine working because the custom entries are not there.

Yes you are right. Before the upgrade to version 2.2.6,
the PFSense was fine. We only have upgraded the PFSense
to the latest version, but didn't changed anything in the configuration.

After the upgrade the IPSec tunnel was disconnect every two
days in the morning and the detection of the gateway had also
a delay.

Now i try to find out, if the latest version of PFSense has a bug
or the modem of the ISP is defect. But i still think that the
PFSense has a bug, because the IPSec issue did not occur
in the versions before.

I have checked both PFSense firewalls and found out that
the option "Disable Gateway Monitoring" is not checked on
both Firewalls.

If i understand it correctly, the option only means that the
WAN IP will not be monitored again. That would be a workaround
to get no warnings in the system logs, but the issue would not fixed
by this.

Something is trying to get from the internal LAN through the WAN interface to connect in
the DMZ or LAN homed Servers and there are no rules for NAT reflection (Hairpin NAT)
could this be a problem too?

IPSEC: One or more IPsec tunnel endpoints has changed its IP. Refreshing.

Is there in the other LAN perhaps something likes an enabled DHCP Server that is giving
new IP addresses to servers or other devices that should be sorted more with static IP addresses?